Q. How many logical processors does Hyper-V R2 support?

A. In beta versions, Windows Server 2008 R2's Hyper-V supported up to32 logical processors. The release candidate and release to manufacturing versions will support up to 64 logical processors, which puts the hypervisor in a good position as new processors with eight cores are released.

In Windows Server 2008, Hyper-V supported up to 16 logical processors. Update KB95670 for Server 2008 added support for up to 24 logical processors.